1. Field of the Invention
The present invention relates to a method for packaging surface mounted devices, and more particularly to modeling a ball grid array (BGA) for inspecting BGA applied electronic devices.
2. Discussion of Related Art
The on-chip delay of signals communicating among components within IC semiconductor devices has been reduced rapidly in the past few years. However, the signal delay in packaged ICs has not been reduced as much as that of the on-chip ICs. This is partly due to the focus of semiconductor industry on fabrication process rather than packaging. Packaging signal loss can be reduced by increasing the packaging density. To this end, a new chip packaging technology called ‘Ball Grid Array’ (BGA) was developed. With BGA chips, more electrical connections between chips and printed boards can be made because the electrical connections are on the under-side of the chip, freeing up more space than the conventional chips having surround edge connections.
There are many ways to inspect BGA chips. Inspection by illumination inspection, a low-power lens or stereo microscope is the most common. Two dimensional (2-D) systems using a camera to capture and digitize the optical image into a gray scale image represent an improvement over aided human vision. Three dimensional surface illumination systems generally use either structured light or laser scanning to generate height information along with a gray-scale image. While these systems tend to provide more surface data for analysis, they tend to be less sensitive to lighting conditions. The disadvantage of BGA packaging is that visual inspection is no longer available because, once the chip is attached to the circuit board, the electrical connections are hidden under the package. An automated x-ray inspection system that uses cross-sectional images to analyze both single-sided and double-sided surface mount assembly circuit cards has been developed for inspecting hidden parts of the package. However, the automated x-ray inspection system is elaborate and complicated. Further, a common problem of the inspection methods and systems described above is that a comparatively large amount of time is needed to inspect all BGA components.
Instead of an X-ray inspection system, an accurate model of the BGA package can be used to facilitate inspection of the BGA package. A need, therefore, exists for an accurate model of the BGA, having information about the geometric structures and properties of the SMD component.